In vehicles, there are automatic transmissions to convert driving force of an engine according to a driving state of the vehicle, and power transmission devices including a transfer and others to transmit the driving power.
The automatic transmission includes one in which a normal gear-type manual transmission is automated to improve transmission efficiency of driving force with respect to the normal-type automatic transmission. The automatic transmission based on the gear-type manual transmission includes different speed-gears having a plurality of gear trains between input and output shafts, and a clutch to transmit driving force on a driving force path from the input shaft to the output shaft so as to change gears while the clutch is transmitting the driving force from the input shaft to the output shaft, thereby reducing disconnection of acceleration torque.
Such an automatic transmission is disclosed in, e.g., JP Laid-Open Nos. 2001-227599, 2001-289288, H06-201027, 2001-280495, and Japanese Utility Model Laid-Open No. H05-96617.
According to JP Laid-Open No. 2001-227599, in an automatic transmission based on the manual transmission, a plurality of mounting shafts including gears defining gear trains, is provided with an intermediate shaft at a position other than an axis line, and a sub clutch is disposed on the intermediate shaft to variably control transmitted torque during shifting gears.
According to JP Laid-Open No. 2001-289288, in an automatic transmission, a main shaft, a countershaft, and first and second sub shafts are disposed in parallel. The main shaft has a first gear thereon to transmit torque of the main shaft through a second passage to the countershaft. The second sub shaft has a third gear thereon to transmit the torque of the main shaft through a third passage to the countershaft. The first and third gears are disposed within a first plane extending perpendicularly to the shafts. The main shaft also has a second gear thereon to transmit the torque of the main shaft through a first passage to the countershaft. The second sub shaft also has a fourth gear thereon to transmit the torque of the main shaft through the third passage to the countershaft. The second and fourth gears are disposed within a second plane extending perpendicularly to the shafts.
According to JP Laid-Open No. H06-201027, an automatic transmission based on the manual transmission includes a damper clutch disposed at an end of an input shaft toward an engine, and a clutch having multi-plates disposed at the other end of the input shaft away from the engine. During shifting gears, variation in vehicle speed can be reduced by using the clutch having multi-plates, and the gears on the input and output shafts.
According to JP Laid-Open No. 2001-280495, a manual transmission has a parking gear on a countershaft outside of a transmission case so as to commonly use existing components of the transmission.
According to Japanese Utility Model Laid-Open No. H05-96617, in a transmission case of a gear transmission, a receiving section to receive lubricating oil is defined in or adjacent to an inner wall toward a portion where the lubricating oil is moved upwardly by gears. A return passage is formed adjacent to another wall that does not have the receiving section so as to downwardly return the lubricating oil received in the receiving section and to supply the oil to the section needed to be lubricated.
In the conventional automatic transmission, mounted on an FF (front engine, front drive) vehicle, in which the normal gear-type manual transmission is automated and a certain gear is engaged while using a hydraulic clutch, an additional hydraulic clutch and oil pump for cooling are equipped in order to reduce disconnection of acceleration torque during shifting gears. This increases the length, which is inconvenience when mounting on the vehicle. In addition, the additional oil pump complicates the constitution of the shafts. Forming a passage for cooling oil also complicates the constitution of the transmission case.
Furthermore, in JP Laid-Open No. H06-201027, positioning of the clutch at the other end of the input shaft away from the engine increases the length of the automatic transmission by the thickness of the clutch. It is difficult to mount the transmission on the vehicle due to interference with the vehicle frame when the engine and transmission are transversely mounted on the vehicle.
To obviate or minimize the above inconvenience, the present invention provides an automatic transmission having change gears including a plurality of gear trains between input and output shafts, and a clutch to transmit driving force on a driving force path between the input and output shafts, the gear trains being shifted while the clutch is transmitting the driving force of the input shaft to the output shaft. In this automatic transmission, the change gears include a first path to directly transmit torque of the input shaft to the output shaft, and a second path to transmit the torque through an intermediate shaft on the driving force path from the input shaft to the output shaft. The first path includes at least one output gear on the output shaft which is engageable and disengageable by a sleeve. The output gear is connected downstream thereof to the second path. The second path includes a first intermediate gear on the intermediate shaft to input the torque, the clutch, and a second intermediate gear rotatably supported through the clutch to output the torque. The output shaft includes a middle speed output gear to mesh with the second intermediate gear so as to form a middle-speed change gear.
According to the present invention, the middle speed gear train also serves as a gear train to drive the intermediate shaft having the clutch. The overall length of the automatic transmission can be reduced by the thickness of both the drive gear dedicated to drive the intermediate shaft and the clutch, so that the automatic transmission can be miniaturized. The interference with the vehicle frame can be eliminated when the engine and the automatic transmission are mounted to the FF (front engine, front drive) vehicle or are mounted transversely.